Power-plant systems include fuel cell systems. Fuel cell systems are increasingly used as power sources in a wide variety of applications. Fuel cell propulsion systems have also been proposed for use in vehicles as a replacement for internal combustion engines. The fuel cells generate electricity that is used to charge batteries and/or to power electric motors. A solid-polymer-electrolyte fuel cell includes a membrane that is sandwiched between an anode and a cathode. To produce electricity through an electrochemical reaction, a fuel, commonly hydrogen (H2), but also either methane (CH4) or methanol (CH3OH), is supplied to the anode and an oxidant, such as oxygen (O2) is supplied to the cathode. The source of the oxygen is commonly air.
In a first half-cell reaction, dissociation of the hydrogen (H2) at the anode generates hydrogen protons (H+) and electrons (e−). The membrane is proton conductive and dielectric. As a result, the protons are transported through the membrane. The electrons flow through an electrical load (such as the batteries or electric motors) that is connected across the membrane. In a second half-cell reaction, oxygen (O2) at the cathode reacts with protons (H+), and electrons (e−) are taken up to form water (H2O).
Hydrogen storage is a key enabling technology for the advancement of fuel cell power systems in transportation, stationary, and portable applications. Absorptive hydrogen storage systems have been developed where hydrogen is absorbed directly into a bulk storage material. Such bulk storage materials include metal hydrides. In simple crystalline metal hydrides, absorption occurs by the incorporation of atomic hydrogen into interstitial sites in the crystallographic lattice structure. More specifically, the metal hydride is charged by injecting hydrogen at elevated temperature and/or pressure into a container filled with metal hydride particles. The hydrogen bonds with the material and releases heat in the process.